There is an ever-increasing need in the electronics industry for low profile and economical means for interconnecting electrical circuits. Traditionally, interconnecting means have required the use of housings, contact terminals, and in many cases, solder. Elastomeric connectors are also used, particularly for connecting components such as liquid crystal displays (LCDs). The present invention eliminates the need for housings, contact terminals and solder for many applications. The invention also eliminates the need for elastomeric connectors and their associated pressure sustaining assemblies.
A large number of printed circuit boards, membrane switches, and the like are used by the electronic industry.
The invention as disclosed herein provides a means for mechanically and electrically interconnecting conductive circuit traces or areas on one substrate with desired conductive circuit traces or areas on a second substrate. The circuitry may be placed on the substrates by a variety of techniques including etching and printing. The interconnecting means is made by applying a layer of an anisotropically conductive adhesive over the surface of the conductive traces or areas and the insulating substrate. The anisotropically conductive adhesive is comprised of a mixture of conductive particles in a nonconductive adhesive binder. Suitable anisotropically conductive adhesive compositions are disclosed in our copending U.S. patent application Ser. No. 601,836 filed Apr. 19, 1984 which is incorporated by reference herein. A layer of thermoplastic or heat activated insulating adhesive is then deposited over the surface of the anisotropically conductive adhesive and in particular to those areas which will be interconnected to conductive areas on another substrate. Interconnection is effected by positioning the desired areas in an overlapping conducting relationship such that the thermoplastic layer is disposed between the two conductive areas. Heat and pressure are applied to the aligned areas thus causing the thermoplastic layer to soften and flow from the aligned areas, and expose the conductive particles in the anisotropically conductive adhesive, thereby interconnecting said conductive areas. Concomitantly, the surrounding areas of substrate are bonded by the adhesive.
Use of the anisotropically conductive adhesive covered with the thermoplastic layer offers many advantages. The anisotropically conductive adhesive can be distributed over the entire surface of the substrate. The conductive particles are sufficiently separated from each other so that current will not flow between adjacent conductive areas on the same substrate. The anisotropically conductive adhesive and thermoplastic adhesive can be used on a variety of surfaces.
In one embodiment, the interconnection means is comprised of a continuous strip of flexible film having a plurality of parallel conductive traces deposited thereon, the surfaces of said traces being essentially covered by the anisotropically conductive adhesive and a layer of dielectric thermoplastic adhesive to form a flexible cable connector. The flexible cable connector can be cut to length and adhered to a second substrate anywhere along its length since the interconnecting capability is present at all points along the cable but is not activated until heat and pressure are applied.
The invention as disclosed herein is particularly useful for point-to-point matrix interconnections. Such interconnections can be made to any exposed conductive traces or areas or with other conductive areas having the anisotropically conductive adhesive and thermoplastic insulating layers in accordance with the invention.
Interconnecting means made in accordance with this invention offer connecting capabilities within the circuit path or area itself thus permitting direct connections between two surfaces without need for a housing. This is particularly advantageous when used on glass or other non-crimpable surfaces. Furthermore, these interconnecting means are particularly suitable for automatic assembly processes. In accordance with the invention these interconnecting means offer discrete and mass termination capabilities. If desired, the circuits can be terminated with standard connectors. Another means for interconnecting conductive circuit traces or areas on two substrates where at least one substrate has screened circuitry is disclosed in our copending U.S. patent application Electrical Interconnecting Means Ser. No. 657,851, filed Oct. 4, 1984.
The interconnecting means disclosed herein can also be used for surface mounting components to a substrate. The means is especially suitable for mechanically and electrically mounting leadless components to either flexible or firm substrates.